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Congenital Sucrase-Isomaltase Deficiency (CSID)

Congenital sucrase-isomaltase deficiency is a disorder that affects a person's ability to digest certain sugars. People with this condition cannot break down the sugars sucrose and maltose. Sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains) are called disaccharides because they are made of two simple sugars. Disaccharides are broken down into simple sugars during digestion.

Sucrose is broken down into glucose and another simple sugar called fructose, and maltose is broken down into two glucose molecules. People with congenital sucrase-isomaltase deficiency cannot break down the sugars sucrose and maltose, and other compounds made from these sugar molecules (carbohydrates).

Congenital sucrase-isomaltase deficiency usually becomes apparent after an infant is weaned and starts to consume fruits, juices, and grains. After ingestion of sucrose or maltose, an affected child will typically experience stomach cramps, bloating, excess gas production, and diarrhea. These digestive problems can lead to failure to gain weight and grow at the expected rate (failure to thrive) and malnutrition. Most affected children are better able to tolerate sucrose and maltose as they get older.

The prevalence of congenital sucrase-isomaltase deficiency is estimated to be 1 in 5,000 people of European descent. This condition is much more prevalent in the native populations of Greenland, Alaska, and Canada, where as many as 1 in 20 people may be affected.

Genetic change

Mutations in the SI gene cause congenital sucrase-isomaltase deficiency. The SI gene provides instructions for producing the enzyme sucrase-isomaltase. This enzyme is found in the small intestine and is responsible for breaking down sucrose and maltose into their simple sugar components. These simple sugars are then absorbed by the small intestine. Mutations that cause this condition alter the structure, disrupt the production, or impair the function of sucrase-isomaltase. These changes prevent the enzyme from breaking down sucrose and maltose, causing the intestinal discomfort seen in individuals with congenital sucrase-isomaltase deficiency.

Inheritance pattern

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Source: National Library of Medicine (NLM)

The disease is probably often missed or misdiagnosed and may be confused with a number of other diseases if not tested for specifically. Examples of differential diagnosis are congenital intestinal malformations, infectious and postinfectious diseases, lactose intolerance, endocrine disorders, pseudomembranous colitis, coeliac disease and cystic fibrosis.

Today it is possible to conduct a gene test which detects the most common mutations in the genes coding for the enzyme sucrase-isomaltase. An alternative is to take a biopsy from the upper smaller intestine and measure the sucrase-isomaltase activity.

The treatment of CSID involves a strict and life-long “table sugar” (sucrose) free diet. However, today this is very difficult to adhere to as much of the processed food we can buy today contains “table sugar” (sucrose) and especially among children the adherence to a diet free from “table sugar” (sucrose) might be problematic.

In USA there is an approved pharmaceutical enzyme replacement therapy which can be used to compensate for the lack of an endogenous functioning enzyme. Such supplementation allows a more normal diet, including some intake of “table sugar” (sucrose) without the development of symptoms.

New research links genetic defects in carbohydrate digestion to irritable bowel syndrome

Irritable bowel syndrome (IBS) affects a large portion of the general population. New research coordinated by Karolinska Institutet now shows a link between defective sucrase-isomaltase gene variants and IBS. Irritable bowel syndrome (IBS) affects a large portion of the general population. New research coordinated by Karolinska Institutet now shows a link between defective sucrase-isomaltase gene variants and IBS.Irritable bowel syndrome (IBS) is the most common gastrointestinal disorder. More than 10% of the population suffer from recurrent symptoms including abdominal pain, gas, diarrhea and constipation. What causes IBS is largely unknown, and this hampers the development of effective treatment for many patients.

Now an international research team led by scientists from Karolinska Institutet in Sweden have identified defective sucrase-isomaltase gene variants that increase the risk of IBS. The study is published in the scientific journal GUT.

The researchers studied DNA variants in the gene encoding the enzyme sucrase-isomaltase (SI), due to the observation that SI mutations are often found in hereditary forms of sucrose intolerance, whose main characteristics diarrhea, abdominal pain and bloating are also common in IBS.

1887 participants studied

By screening 1887 study participants from multiple centers in Sweden, Italy and US, they found that rare defective SI mutations were twice more common among IBS cases than healthy controls, and a common variant with reduced enzymatic activity was also associated with increased risk of IBS.

“A significant decrease in the enzymatic activity of sucrase-isomaltase would be compatible with poor carbohydrate digestion in the intestine, possibly leading to malabsorption and bowel symptoms” says co-senior author Hassan Naim from the University of Veterinary Medicine Hannover.

In addition to Karolinska Institutet and the University of Veterinary Medicine Hannover, researchers and clinicians from several other institutions participated in the study, including the Mayo Clinic and University of California Los Angeles in the US, Christian-Albrechts-University Kiel in Germany, BioDonostia Health Research Institute in San Sebastian Spain, the University of Bologna Italy, and others.

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